This invention related to a surface rewinder and method and, more particularly, to a rewinder wherein the closed loop operation of one of the drums minimizes drum to web slippage.
In the past, two basic types of surface rewinders have been available commercially. One type of surface rewinder is seen in a co-owned U.S. Pat. No. 4,909,452 and features a movable winding drum. More particularly, the transition of the core and partially wound product from one side of the nip of the winding drums to the other is done with a combination of lower drum movement, infeed transfer finger exposure and speed differential between the two drums. At the beginning of the cycle the distance between the two winding drums is very quickly dropped. The infeed transfer fingers are then proportionately exposed and this, along with a small speed differential between the drums, quickly drives the product from one side of the drums' nip to the other. This allows the diameter of the product to build and move through the nip from one side to the other without additional compression. Thereafter, the speed differential remains constant.
Another surface rewinder can be seen in U.S. Pat. No. 4,327,877. This uses a speed change of one of the rolls also to quickly move the core and product partly wound thereon from one side of the pair of winding rolls to the other. This method compresses the product while the speed change advances the product. In operation, the lower drum speed quickly slows by controlled deceleration and then returns to the upper drum speed through the remainder of the wind cycle.
In each case, there is a degree of dependency on slippage between the product and the surfaces in contact therewith. If the drum surfaces are smooth enough to allow slippage, they also permit unstable products (typically soft rolls) which easily bounce around in the three drum winding area limiting the speed at which they can be run. Alternatively, smooth webs permit slippage but roughness results in bounces--see U.S. Pat. No. 1,719,830.
According to the invention in my earlier application noted above, the three drum cradle includes spaced apart first and second winding drums with control means operably associated with the drums for changing the rotational speed of one drum to substantially eliminate slippage. This was done by providing a speed profile wherein the speed of one of the winding drums was decreased in the beginning of each winding cycle to advance a partially wound roll through the space between winding drums and thereafter increasing the speed of the specific drum as a function of the increasing diameter of the partially wound roll.
The instant invention provides other ways of minimizing slippage in a surface winder. In one advantageous embodiment, this is achieved by moving one of the drums through an orbit or closed loop--and this is possible without varying the speed of either of the winding drums. However, the orbiting drum approach is also advantageous with a speed profile on one of the drums. The orbiting movement is advantageously applied to one of the winding drums and, alternatively or cumulatively, to the rider drum. And either or both drums can benefit from the previously-referred to speed profile.
Another embodiment employs the basic speed profile described in my earlier application but modifies the same to provide a selected portion in the completed log of a different tension, i.e., a portion at one radial position that can be either "harder" or "softer" than another portion. Certain converters and certain customers have different requirements which are thus easily met by modifying the speed profile determined by the winder controller. For example, a harder annulus near the core can prevent core collapse while a harder annulus adjacent the periphery aids in maintaining a constant diameter.
Other objects and advantages of the invention may be seen in the details of construction and operation set forth in the ensuing specification.